2012 International Conference on Industrial and Intelligent Information (ICIII 2012)
IPCSIT vol.31 (2012) © (2012) IACSIT Press, Singapore
Mixture of Anionic Extended Surfactant and Cationic Surfactant:
Precipitation and Critical Micelle Concentration
Phakawadee Archawapanich 1∗, David A. Sabatini2 and Sutha Khaodhiar3
1
2
National Research Center, Environmental Hazardous Waste Management, Chulalongkorn University,
Bangkok, Thailand
Civil Engineering and Environmental Science Department, Carson Engineering Center and Institute for
Applied Surfactant Research (IASR), Sarkeys Energy Center, The University of Oklahoma,
Norman, Oklahoma
3
Engineering Department, Chulalongkorn University, Bangkok, Thailand
Abstract. This research study the precipitation and the critical micelle concentration(CMC) of three
sulfated-based anionic extended surfactants and one pyridinium-based cationic surfactant mixtures to
improve efficiency of surfactant-based groundwater remediation. Cetylpyridinium Chloride was used as
cationic surfactant and Alkyl propoxylated sulfate surfactant with difference in number of propylene
oxide(PO) group (4 and 8) and/or number of carbon chain length (C14-15 and C16-17). For the precipitation
studies, Mixed surfactants greatly help reducing precipitation regions when compare with conventional
surfactant. For the CMC of the propoxylated sulfate extended surfactants, C14,15(PO)4SO4Na,
C16,17(PO)4SO4Na and C14,15(PO)8SO4Na, are 0.038, 0.019, 0.015 mM, respectively while the CMC of mixed
system are 0.0013, 0.0010, 0.0011 mM, respectively. Moreover, the results show that CMC values of mixed
system are lower when compared with conventional surfactant/CPC or even with each extended surfactant
itself.
Keywords: precipitation, critical micelle concentration(CMC), extended surfactant, mixed surfactant,
propylene oxide(PO).
1. Introduction
Non-aqueous phase liquids (NAPLs) are one of the major environmental concerns. These compounds are
hydrocarbons which have limited water solubility and present as immiscible phase when contact with water.
To overcome with these problems, surfactant-based remediation techniques have been widely used as
alternative technologies. Mixtures of anionic and cationic surfactants have been considered as one of a
efficient way of remediation technique. There are the great advantages of using the mixed anionic and
cationic surfactants, for examples, they can reduce interfacial tension (IFT), reach the lower CMC than the
individual anionic or cationic surfactants [1] and also produce microstructure [2]. Although the mixed
anionic and cationic surfactants can induce high efficiency in solubilization, they still have some limitations
to consider. Generally, mixture of anionic and cationic surfactant system can not be presented in the same
formulation due to the crystalline precipitation [2]. The tendency to form precipitates or liquid crystaline
phases is the main drawback of anionic and cationic surfactant mixture system which affects to surfactant
∗
Phakawadee Archawapanich. Tel.: + 66814303452; fax: +6625179839.
E-mail address: pachoo_@hotmail.com.
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usage in many applications such as detergency performance and subsurface remediation of oil contamination
[3-5].
The extended surfactants have been recently developed to enhance the solubilization of organic solutes
because the dominant characteristic of these surfactants are the presence of one or more intermediate-polarity
groups between the hydrophilic head and the hydrophobic tail.
Therefore, in this research, the synergism of sulfated-based anionic extended surfactants and pyridiniumbased cationic surfactants mixtures will be studied and compared to the previous systems.
2. Objectives
• To evaluate the precipitation phase boundary of mixtures of sulfated-based anionic extended
surfactant (C14,15(PO)4SO4Na, C16,17(PO)4SO4Na and C14,15(PO)8SO4Na) and pyridinium-based
cationic surfactant (Cetylpyridinium Chloride), to define appropiate concentration regimes in which
to conduct the adsorption studies.
• 2. To investigate the critical micelle concentration of individual surfactant system and mixed
surfactant system (anionic extended surfactants and cationic pyridinium surfactant) by measuring
surface tension versus surfactant concentration.
3. Materials and Methodology
3.1. Materials
Surfactants used in this research are anionic sulfated extended surfactants and pyridinium-based cationic
surfactant.
• Anionic extended surfactants: Anionic extended surfactants used in this research are alkyl branched
propoxylated sulfates of Alfoterra® series which vary in carbon chain length of either 14 and 15 or 16
and 17, and different moles of propylene oxide (PO) group (3, 4 and 8 moles). These surfactants were
donated from Sasol North America Inc. (LA, USA).
• Cationic surfactant: Cetylpyridinium Chloride (CPC, 98% purity), selected as cationic surfactant with
a C16 alkyl chain length, was purchased from Fluka Chemical Company Ltd. (Buchs, Germany). The
properties of studied surfactants are shown in Table 1.
Table 1 Surfactant properties
MW
Number of carbon
in alkyl chain
Formula
Alkyl propoxylated sulfate C14,15-3PO
483
14-15
C14,15(PO)3SO4Na
Alkyl propoxylated sulfate C14,15-4PO
554
14-15
C14,15(PO)4SO4Na
Alkyl propoxylated sulfate C16,17-4PO
578
16-17
C16,17(PO)4SO4Na
Alkyl propoxylated sulfate C14,15-8PO
715.5
14-15
C14,15(PO)8SO4Na
358.01
16
Surfactant
Anionic Extended Surfactants
Cationic Surfactant
Cetylpyridinium Chloride
PO: Propylene oxide (C3H6O)
3.2. Methodology
3.2.1. Precipitation Study
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C21H38ClN
The stock solutions of mixed surfactant were prepared as series of samples in 15 mL vials with Teflonlined caps (Fisher Scientific, Denver, CO). The electrolyte concentration was controlled at 1 mM NaCl.
NaOH and HCl were used to adjust solution pH at 7.0±0.5. The samples were precipitate at 0° C for 2 days
to avoid supersaturation effects. Then these samples were kept at room temperature of 25±2°C and shaken
periodically for one week. The presence of precipitate and undesirable phase in solution were examined by
visual inspection with high intensity light.
3.2.2 CMC Measurements
The CMC of the individual and mixed surfactant systems were determined using a Wilhelmy plate
tensiometer (DCAT 11, Data Physics, Filderstadt, Germany). The experiments were performed at room
temperature (25±2°C) and electrolyte concentration of 1 mM. The surface tension versus the logarithm of the
total surfactant concentration were plotted. Then the CMC of each surfactant was indicated by a sharp
change in the slope of the plotted point.
4. Results and Discussion
4.1. Result of the precipitation at 1mM NaCl
Figure 1 presents the precipitation phase boundary of anionic extended surfactants and cationic
surfactant at 1 mM of NaCl. The results show that there is extremely reduction in the precipitation regions of
mixed system when compared with mixed system of conventional surfactant. In addition, from the
precipitation diagram, the lower number of PO group and/or longer carbon chain length takes effect to
increase precipitation phase boundary.
At 1 mM NaCl
Fig. 1: Precipitation diagrams for mixed surfactant systems at 1 mM NaCl
4.2. Results of the CMC study of the individual surfactant and the mixed surfactant at 1
mM NaCl
The CMC of surfactant system is defined as the breakpoint plateau in the graph of surface tension versus
logarithm of surfactant concentration as shown in figure 2-5.
In the individual surfactant system, the CMC of CPC is the highest. The CMC of C14,15(PO)4SO4Na,
C16,17(PO)4SO4Na and C14,15(PO)8SO4Na are 0.038, 0.019, 0.015 mM, respectively. The CMC decreases with
increasing number of PO group for the surfactant with the same number of carbon of carbon in alkyl chain
because of the higher hydrophobicity in surfactant molecule. Moreover, the CMC also decreases with
increasing number of carbon in alkyl chain for surfactant with the same number of PO group due to the same
reason. The results from Figure 2 indicate that the CMC of C16,17(PO)4SO4Na and C14,15(PO)8SO4Na are not
significantly different.
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In the mixed surfactant system, the CMC of all individual systems are higher than mixed systems about
ten times due to synergism effect. The CMC of C14,15(PO)4SO4Na/CPC, C16,17(PO)4SO4Na/CPC and
C14,15(PO)8SO4Na/CPC are 0.0013, 0.0010, 0.0011 mM, respectively. The results from Figure 2 indicate that
the C14,15(PO)4SO4Na/CPC, C16,17(PO)4SO4Na/CPC and C14,15(PO)8SO4Na/CPC are not significantly different.
Figure 3-5 provide the graphical results of mixed system. The values of CMC for both individual surfactant
system and mixed surfactant system are summarized in Table2.
Fig. 2: Surface Tension of individual surfactants
At 1 mM NaCl
Fig. 3: Surface Tension of CPC, C14,15(PO)4SO4Na and C14,15(PO)4SO4Na /CPC(1:5 molar ratio)
At 1 mM NaCl
At 1 mM NaCl
Fig. 4: Surface Tension of CPC, C16,17(PO)4SO4Na
and C16,17(PO)4SO4Na /CPC(1:5 molar ratio)
Fig. 5: Surface Tension of CPC, C14,15(PO)8SO4Na
and C14,15(PO)8SO4Na /CPC(1:5 molar ratio)
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Table 2 CMC values and properties of individual surfactant system and mixed surfactant system , temperature 25±2 °C,
pH 7.0±0.5 and 1mM NaCl at liquid-air interface
Surfactants
CMC(mM)
Slope
R2
Individual system
Cetylpyridinium Chloride(CPC)
0.66
-7.51
0.99
Alkyl propoxylated sulfate C14,15-4PO
0.038
-8.93
0.98
Alkyl propoxylated sulfate C16,17-4PO
0.019
-11.32
0.97
Alkyl propoxylated sulfate C14,15-8PO
0.015
-7.88
0.98
Alkyl propoxylated sulfate C14,15-4PO/CPC
0.0013
-6.87
0.99
Alkyl propoxylated sulfate C16,17-4PO/CPC
0.0010
-8.72
0.99
Alkyl propoxylated sulfate C14,15-8PO/CPC
0.0011
-9.25
0.99
Mixed system (In 1:5 Molar ratio)
5. Conclusions
The extended surfactant can effectively reduce the tendency to precipitate of surfactant when compare
with conventional surfactant. The mixed ratio of anionic-cationic surfactants used in adsorption studies is 1:5
since it was ensured to be outside precipitation regions. According to the CMC results, the extended
surfactant had very low critical micelle concentration. In addition, the numbers of PO groups and carbon
chain length take effect to CMC value that CMC decreases with increasing number of PO and/or longer
carbon chain length.
For CMC study of individual surfactant, very low critical micelle concentration of extended surfactants
corresponds to theory. In addition, the numbers of PO groups and carbon chain length take effect to CMC
value. Increasing PO numbers and/or longer carbon chain length results in lower CMC. Moreover, the results
show that higher number of PO group, 4PO and 8PO, take similar effect to longer in carbon chain length 1415 and 16-17 carbon chain length.
For CMC study of mixed surfactant, CMC of all mixed surfactants are lower than CMC of individual
surfactants but CMC of three mixed systems are not significantly different. Nevertheless, Characteristics of
surface tension at liquid-air interface versus surfactant concentration graph is not the same as regular graph
because surface tension still decrease after it seems to reach plateau. This reason may cause the mixed
surfactants in systems are unstable, micelle forms may be convertible depending on time and/or
concentration, moreover, the change in slope after reaching CMC of the mixture may be affected by CMC of
each individual surfactant system itself.
6. Acknowledgement
Financial support for this work was provided by the National Center of Excellent for Environmental and
Hazardous Waste Management (NCE-EHWM), Chulalongkorn University, Thailand.
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7. References:
[1] Mehreteab A (1999) Anionic-Cationic Surfactant Mixtures. In: Broze G (ed) Handbook of Detergents, Part A:
Properties. Marcel Dekker, New York, pp 133-136
[2] Kume G, Gallotti M, and Nunes G (2008) Review on Anionic/Cationic Surfactant Mixtures. J Surfact Deterg 11:
1-11
[3] Stellner KL, Amante JC, Scamehorn JF, Harwell JH (1988) Precipitation Phenomena in Mixtures of Anionic and
Cationic Surfactants in Aqueous Solutions. J Colloid and Interface Sci 123:186-200
[4] Rodriguez CH, Lowery LH, Scamehorn JF, and Harwell JH (2001). Kinetics of Precipitation of Surfactants. I.
Anionic Surfactants with Calcium and with Cationic Surfactants. J Surfact Deterg. 4:1-14
[5] Rodriguez CH, Scamehorn, JH (2001) Kinetics of Precipitation of Surfactants. II. Anionic Surfactant Mixtures. J
Surfactants Deterg. 4:15-26
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